High definition television transmission with mobile capability

ABSTRACT

A method and architecture for processing signal communications between an encoder and decoder operating according to the ATSC standard adapted for mobile handheld transmission is disclosed. The method and apparatus comprises embedding code rate identifiers in the packet ID and training sequences, using a chirp sequence as a training sequence and transmitting data in a single burst wherein the data is encoded according to multiple code rates.

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional PatentApplication No. 60/998,978 entitled “High Definition TelevisionTransmission with Mobile Capability” and No. 60/999,040 entitled“Physical Layer Control Block for Mobile VSB Submission” and No.60/998,961 entitled “High Definition Television Transmission Including aMode For Mobile Operation”, which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to transmitting data in a multimodetransmission system. In particular, the present invention relates to atransmission system wherein multiple code rates can be used in datatransmission within a single standard transmission protocol, such asATSC.

BACKGROUND OF THE INVENTION

Over the past decades, video transmission systems have migrated fromanalog to digital formats. In the United States, broadcasters are in thefinal stages of completing the switch from the National TelevisionSystem Committee (NTSC) analog television system, to the AdvancedTelevision Systems Committee (ATSC) A/53 digital television system. TheA/53 standard provides “specification of the parameters of the systemincluding the video encoder input scanning formats and the preprocessingand compression parameters of the video encoder, the audio encoder inputsignal format and the pre-processing and compression parameters of theaudio encoder, the service multiplex and transport layer characteristicsand normative specifications, and the VSB RF/Transmission subsystem.”The A/53 standard defines how source data (e.g., digital audio and videodata) should be processed and modulated into a signal that is to betransmitted over the air. This processing adds redundant information tothe source data so that a receiver may recover the source data even ifthe channel adds noise and multi-path interference to the transmittedsignal. The redundant information added to the source data reduces theeffective rate at which the source data is transmitted, but increasesthe potential for successful recovery of the source data from a receivedsignal.

The ATSC A/53 standard development process was focused on HDTV and fixedreception. The system was designed to maximize video bit rate for thelarge high resolution television screens that were already beginning toenter the market. Transmissions broadcast under the ATSC A/53 standard,however, present difficulties for mobile receivers. Enhancements to thestandard are required for robust reception of digital television signalsby mobile devices.

Recognizing this fact, in 2007, the ATSC announced the launch of aprocess to develop a standard that would enable broadcasters to delivertelevision content and data to mobile and handheld devices via theirdigital broadcast signal. Multiple proposals were received in response.The resulting standard, to be called ATSC-M/H, is intended to bebackwards compatible with ATSC A/53, allowing operation of existing ATSCservices in the same RF channel without an adverse impact on existingreceiving equipment.

Many systems for transmission to mobile devices, such as some proposedATSC-M/H systems, perform periodic transmission. Such systems caninclude a preamble in their transmissions in order to assist withreceiver system operation. Preambles typically include known informationthat portions of the receiving system may use for training to improvereception, which can be particularly useful in difficult environmentssuch as those found in mobile operation. Such systems may further encodedata at differing code rates. The code rate or information rate of aforward error correction (FEC) code, for example a convolutional code,states what portion of the total amount of information that is nonredundant. The code rate is typically a fractional number. If the coderate is k/n, for every k bits of useful information, the coder generatestotally n bits of data, of which n-k are redundant.

A common problem in multimode transmission systems including a mode thatmay be periodic, and may further include multiple possible transmissionprotocols such as code rates, is identification of transmission protocolwithin the transmission signal, thereby providing significant advantagesto the receiving system. Providing identification typically reduces theefficiency of the data transmission by either requiring a separate datachannel or implementing a receiver which attempts to decode the incomingdata at each possible code rate until the suitable code rate is found.This is a time consuming effort, which prevents the timely acquisitionof data, especially in a system where the code rate may changecontinuously during a data stream. Therefore, a system indicating thecode rate to be used in decoding the data, It is desirable to find anidentification system that does not impact efficiency. thereby avoidingthe need to attempt to decode all the possible code rates is desired.The present invention described herein addresses this and/or otherproblems.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a method forprocessing an signal is disclosed. According to an exemplary embodimenta method for encoding data comprises the steps of encoding said data ina first format and packetizing said data in a packet, said packetcomprising said data and a packet identifier; said packet identifiercomprising an indicator indicating said first format.

In accordance with another aspect of the present invention a method ofprocessing a signal is disclosed. According to an exemplary embodiment,the method for decoding data comprises the steps of receiving a packetcomprising data and a packet identifier, determining a code rate inresponse to a portion of said packet identifier and decoding said dataaccording to said code rate.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of a terrestrial broadcasttransmitter for mobile/handheld reception of the present disclosure;

FIG. 2 is a block diagram of an embodiment of a portion of an exemplarymobile/handheld data stream of the present disclosure;

FIG. 3 is a block diagram of an embodiment of an exemplary data frame ofthe present disclosure;

FIG. 4 is a block diagram of an embodiment of a terrestrial broadcastreceiver for mobile/handheld reception of the present disclosure;

FIG. 5 is a block diagram of an embodiment of a decoder of the presentdisclosure;

FIG. 6 is a block diagram of another embodiment of a decoder of thepresent disclosure;

FIG. 7 is a state diagram of an exemplary embodiment of a method ofencoding according to the present invention.

FIG. 8 is a state diagram of an exemplary embodiment of a method ofdecoding according to the present invention.

FIG. 9 is a state diagram of an additional exemplary embodiment of amethod of encoding according to the present invention.

FIG. 10 is a state diagram of an additional exemplary embodiment of amethod of decoding according to the present invention.

FIG. 11 is a state diagram of an additional exemplary embodiment of amethod of encoding according to the present invention.

FIG. 12 is a state diagram of an additional exemplary embodiment of amethod of decoding according to the present invention.

FIG. 13 is a state diagram of an additional exemplary embodiment of amethod of encoding according to the present invention.

FIG. 14 is a state diagram of an additional exemplary embodiment of amethod of decoding according to the present invention.

FIG. 15 is a state diagram of an additional exemplary embodiment of amethod of encoding according to the present invention.

The exemplifications set out herein illustrate preferred embodiments ofthe invention, and such exemplifications are not to be construed aslimiting the scope of the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As described herein, the present invention provides a method andapparatus for enabling insertion of a code rate identifier in atransmission subsystem for mobile digital television, such as a proposedATSC-M/H system, while allowing backward compatibility with legacytransmission and reception paths, such as ATSC A/53. While thisinvention has been described as having a preferred design, the presentinvention can be further modified within the spirit and scope of thisdisclosure. This application is therefore intended to cover anyvariations, uses, or adaptations of the invention using its generalprinciples. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims. For instance, the describedtechnique could be applicable to transmission systems designed for othertypes of data or that use different coding, error-correction,redundancy, interleaving, or modulation schemes.

Referring now to the drawings, and more particularly to FIG. 1, a blockdiagram of an embodiment of a terrestrial broadcast transmitter formobile/handheld reception of the present disclosure is shown. Embodiment100 of FIG. 1 comprises a plurality of signal transmitting means such asan MPEG Transport stream source 110, an ATSC M/H preprocessing path 115,and a legacy ATSC A/53 processing path. The elements within the ATSC-M/Hpreprocessing 115 comprise a packet interleaver 120, a serialconcatenated block coder 125, a packet deinterleaver 130, an MPEGtransport stream header modifier 135, a preamble packet inserter 140.The legacy ATSC A/53 processing path 145 comprises a data randomizer150, a reed Solomon encoder 155, a byte interleaver 160, a trellisencoder 165, a sync inserter 170, a pilot inserter 175 and a modulator180.

In the ATSC-M/H preprocessing flow, incoming MPEG transport data 112from an MPEG transport stream source 110 is received at the packetinterleaver 120. The packet interleaver 120 rearranges a sequencednumber of bytes into a different sequence to improve bit error rate andframe error rate performance. In this exemplary embodiment, the packetinterleaver 120 takes the bytes from a fixed number of consecutivepackets in a row by row order, and outputs the bytes column by column.In this way, all of the first bytes of the packets are grouped together,all of the second bytes of the packets are grouped together, and so onuntil the last bytes of the packets. Each source packet is an MPEGtransport stream packet with the sync byte removes, so each packetlength is 187 bytes. The number of packets in each code frame is thesame as the number of source symbols required for the GF(256) serialconcatenated block code.

The interleaved data is then coupled to the GF(256) serial concatenatedblock coder (SCBC) 125. The SCBC 125 codes the packet interleaved datain one of a plurality of forms depending on the desired data rate andthe codeword length. The SCBC 125 consists of one or more constituentGF(256) codes cascaded in a serial fashion, linked by GF(256) codeoptimized block interleavers to improve overall code performance. Thismay be optionally followed by a GF(256) puncture to achieved desiredcodeword length.

The data is then coupled to a packet deinterleaver 130. The packetdeinterleaver 130 takes the bytes from the resulting SCBC codewords forthe original group of packets in a column-by-column order, and outputsthe bytes in a row by row order. The original packets are reconstitutedand new packets are created from the parity bytes of the SCBC codewords.Each packet corresponds to a common GF(256) symbol location in all thecreated SCBC codewords. The number of packets created in each code frameis nSCBC, where the first kSCBC packets are the original data packetsand the last (nSCBC-kSCBC) packets are parity packets.

The data is then coupled to the MPEG TS header modifier 135 where theMPEG headers are modified. The MPEG TS header modifier may modify thepacket Identifier (PID) of the MPEG transport stream headers to indicatethe code rate used by the error correction scheme. The code rates isexpressed as a fraction of the original number of data bytes over thetotal number of data bytes used. For example, in a 12/52 rate mode,which supplements 12 data bytes with 40 parity bytes, each group of 12bytes uses one R=1/2 Encoder, and two R=12/26 Encoders, with each 12/26Encoder using two R=2/3 Encoders and one 27/26 puncture, results in a12/52 rate mode The R=27/26 puncture is performed in such a way that thelast byte of the 27 bytes is dropped. Two Data Blocks are used totransmit 12 MPEG TS packets under the 12/52 Rate Mode. The 12/26 ratemode supplements 12 data bytes with 14 parity bytes, each group of 12data bytes uses two R=2/3 Encoders, and one R=27/26 puncture, results ina 12/26 rate mode. The R=27/26 puncture shall be performed in such a waythat the last byte of the 27 bytes is dropped. One Data Block is used totransmit 12 MPEG TS packets under the 12/26 Rate Mode. The 17/26 ratemode supplements 17 data bytes with 9 parity bytes, each group of 17data bytes group uses one R=2/3 Encoder to supplement 16 data bytes with8 parity bytes, and one R=1/2 Encoder to supplement 1 data byte with 1parity byte, results in a 17/26 rate mode. One Data Block is used totransmit 17 MPEG TS packets under the 17/26 Rate Mode. The 24/208 ratemode supplements 24 data bytes with 184 parity bytes, each group of 24data bytes uses 24 R=1/4 Encoders, and eight 12/26 Encodes, results in a24/208 rate mode. The R=27/26 puncture shall be performed in such a waythat the last byte of the 27 bytes is dropped. Eight Data Blocks areused to transmit 24 MPEG TS packets under the 24/208 Rate Mode.

Each packet utilizing the MPEG protocol typically contains a packetidentification portion or PID. The current system allows for over 8000possible unique identification elements, and at present, only 50 areused. The PID is typically one or more bytes of information used foridentifying the type of data in the packet. At present many of the PIDportions of the bits remain reserved and unused. These PIDs can be usedto identify a specific error correction code rate that will be imposedon the packet. Certain rules based on MPEG protocol should be maintainedin order to assure the PID is properly identified by any receivingsystem. A three-byte header 440 contains a 13-bit packet identifier(PID) identifying the packet as part of a mobile/handheld transmission.The headers 440 of MPEG packets from the ATSC-M/H stream are modifiedafter packet-deinterleaving to contain packet identifiers (PIDs) thatare not recognized by legacy ATSC A/53 receivers. Thus, a legacyreceiver should ignore the ATSC-M/H specific data, providing backwardcompatibility.

This data is then coupled to the Preamble packet inserter 140, wherepreamble packets consisting of consecutive MPEG packets are formed intoa preamble block. The MPEG packets are formed with a valid MPEG headerwith data bytes generated from a PN generator (not shown). The number ofdata bytes generated from the PN generator varies with the code rateused, for example, 184 data bytes are generated in 12/52 rate mode toresult in a total of 2208 bytes of PN data. According to an exemplaryembodiment, the PN generator is a 16-bit shift register with 9 feedbacktaps. 8 of the shift register outputs are selected as the output byte.ATSC M/H packets are placed in between Preamble blocks in Data Blocks.Every Data Block contains 26 ATSC M/H encoded packets that have the samecoding or 26 ATSC A/53 encoded packets. Once the preamble packets havebeen inserted 140, the ATSC M/H stream has been formed.

The ATSC-M/H data stream is then processed by the legacy ATSC A/53 path145, including data randomizer 150, Reed-Solomon encoder 155, byteinterleaver 160, 12-1 trellis encoder 165, sync insertion 170, pilotinsertion 175, and modulation 180. In the data randomizer 150, each bytevalue is changed according to known pattern of pseudo-random numbergeneration. This process is reversed in the receiver in order to recoverthe proper data values. With the exception of the segment and fieldsyncs, it is desirable for the 8-VSB bit stream to have a completelyrandom, noise-like nature to afford the transmitted signal frequencyresponse must have a flat noise-like spectrum in order to use theallotted channel space with maximum efficiency.

The data is then coupled to the Reed-Solomon encoder 155, whereReed-Solomon (RS) coding provides additional error correction potentialat the receiver through the addition of additional data to thetransmitted stream. In an exemplary embodiment, the RS code used in theVSB transmission system is a t=10 (207,187) code. The RS data block sizeis 187 bytes, with 20 RS parity bytes added for error correction. Atotal RS block size of 207 bytes is transmitted per RS code word. Increating bytes from the serial bit stream, the MSB shall be the firstserial bit and the 20 RS parity bytes are sent at the end of the datablock or RS code word.

The byte interleaver 160 then processes the output of the Reed-Solomonencoder 155. Interleaving is a common technique for dealing with bursterrors that can occur during transmission. Without interleaving, a bursterror could have a large impact on one particular segment of the data,thereby rendering that segment uncorrectable. If the data is interleavedprior to transmission, however, the effect of a burst error can beeffectively spread across multiple data segments. Rather than largeerrors being introduced in one localized segment that cannot becorrected, smaller errors may be introduced in multiple segments thatare each separately within the correction capabilities of forward errorcorrection, parity bit, or other data integrity schemes. For instance, acommon (255, 223) Reed-Solomon code will allow correction of up to 16symbol errors in each code word. If the Reed-Solomon coded data isinterleaved before transmission, a long error burst is more likely to bespread across multiple codewords after deinterleaving, reducing thechances that more than the correctable 16 symbol errors are present inany particular codeword.

The interleaver employed in a VSB transmission system is a 52 datasegment (intersegment) convolutional byte interleaver. Interleaving isprovided to a depth of about ⅙ of a data field (4 ms deep). Only databytes are interleaved. The interleaver is synchronized to the first databyte of the data field. Intrasegment interleaving is also performed forthe benefit of the trellis coding process.

The signal is then coupled to the Trellis encoder 165. Trellis coding isanother form of Forward Error Correction. Unlike Reed-Solomon coding,which treats the entire MPEG-2 packet simultaneously as a block, trelliscoding is an evolving code that tracks the progressing stream of bits asit develops through time. Accordingly, Reed-Solomon coding is known as aform of block code, while trellis coding is a convolutional code.

In ATSC trellis coding, each 8-bit byte is split up into a stream offour, 2-bit words. In the trellis coder, each 2-bit word that arrives iscompared to the past history of previous 2-bit words. A 3-bit binarycode is mathematically generated to describe the transition from theprevious 2-bit word to the current one. These 3-bit codes aresubstituted for the original 2-bit words and transmitted over-the-air asthe eight level symbols of 8-VSB (3 bits=8 combinations or levels). Forevery two bits that go into the trellis coder, three bits come out. Forthis reason, the trellis coder in the 8-VSB system is said to be a ⅔rate coder. The signaling waveform used with the trellis code is an8-level (3 bit) one-dimensional constellation. The transmitted signal isreferred to as 8 VSB. A 4-state trellis encoder shall be used.

In an exemplary embodiment, trellis code intrasegment interleaving isused. This uses twelve identical trellis encoders and precodersoperating on interleaved data symbols. The code interleaving isaccomplished by encoding symbols (0, 12, 24 36 . . . ) as one group,symbols (1, 13, 25, 37, . . . ) as a second group, symbols (2, 14, 26,38, . . . ) as a third group, and so on for a total of 12 groups.

Once the data has been trellis encoded, it is coupled to the syncinserter 170. The sync inserter 170 is a multiplexer which inserts thevarious synchronization signals (Data Segment Sync and Data Field Sync).A two-level (binary) 4-symbol Data Segment Sync is inserted into the8-level digital data stream at the beginning of each Data Segment. TheMPEG sync byte is replaced by Data Segment Sync. In an exemplaryembodiment using ATSC transmission standards, a complete segment shallconsist of 832 symbols: 4 symbols for Data Segment Sync, and 828 dataplus parity symbols. The same sync pattern occurs regularly at 77.3 sintervals, and is the only signal repeating at this rate. Unlike thedata, the four symbols for Data Segment Sync are not Reed-Solomon ortrellis encoded, nor are they interleaved. The ATSC segment sync is arepetitive four symbol (one byte) pulse that is added to the front ofthe data segment and replaces the missing first byte (packet sync byte)of the original MPEG-2 data packet. Correlation circuits in the 8-VSBreceiver home in on the repetitive nature of the segment sync, which iseasily contrasted against the background of completely random data. Therecovered sync signal is used to generate the receiver clock and recoverthe data.

Segment syncs are easily recoverable by the receiver because of theirrepetitive nature and extended duration. Accurate clock recovery can behad at noise and interference levels well above those where accuratedata recovery is impossible allowing for quick data recovery duringchannel changes and other transient conditions.

After sync insertion, the signal is coupled to the pilot insertion wherea small DC shift is applied to the 8-VSB baseband signal causing a smallresidual carrier to appear at the zero frequency point of the resultingmodulated spectrum. This ATSC pilot signal gives the RF PLL circuits inthe 8-VSB receiver a signal to lock onto that is independent of the databeing transmitted. The frequency of the pilot is the same as thesuppressed-carrier frequency. This may be generated by a small (digital)DC level (1.25) added to every symbol (data and sync) of the digitalbaseband data plus sync signal (+1, +3, +5, +7). The power of the pilotis typically 11.3 dB below the average data signal power.

After the pilot signal is inserted, the data is coupled to the modulator180. The modulator amplitude modulates the 8 VSB baseband signal on anintermediate frequency (IF) carrier. With traditional amplitudemodulation, we generate a double sideband RF spectrum about our carrierfrequency, with each RF sideband being the mirror image of the other.This represents redundant information and one sideband can be discardedwithout any net information loss. In 8 VSB modulation, the VSB modulatorreceives the 10.76 Msymbols/s, 8-level trellis encoded composite datasignal (pilot and sync added). The ATV system performance is based on alinear phase raised cosine Nyquist filter response in the concatenatedtransmitter and receiver, as shown in FIG. 12. The system filterresponse is essentially flat across the entire band, except for thetransition regions at each end of the band. Nominally, the roll-off inthe transmitter shall have the response of a linear phase root raisedcosine filter.

The transmission system includes operation for mobile and portabledevices in a burst mode of transmission. Several key advantages ofoperating in burst mode, are described throughout the above document andinclude ability to be received by a new class of devices while stillmaintaining backward compatibility. These new classes of devices requirea lower level of video resolution than is found in the existingbroadcast standard, and can therefore also allow higher coding andcompression, as well as other features including working in the presenceof higher noise levels. An additional advantage of burst mode types ofoperation is focused on the potential device power savings by focusinguse of the device only when signals intended for the device or to bereceived.

Burst mode operations such as those described may take advantage of timeperiods during which high data transmission of a signal is not requiredin order to maintain full performance of a legacy system and receiver.Burst mode operation may be based on processing signals based on aso-called new information processing rate, which may change depending onthe current broadcast signal characteristics.

Backward compatibility with the legacy system is maintained by focusingthe burst mode operations at a data packed level by introducinginformation for new program identifiers. The new program identifiersallow the new class of equipment to recognize the data, withoutaffecting the operation of existing equipment. Further legacy supportexists by including an Overlay structure in order to maintain legacysignal transmission operation during certain burst mode profiles.

Referring to FIG. 2, a block diagram of an embodiment of a portion of anexemplary mobile/handheld data stream 200 of the present disclosure isshown. 26 ATSC M/H coded packets are grouped into 1 Data Block. Inlegacy ATSC transmission every Data Block typically has the same coding,although this is not physically required. Preamble blocks are two blockslong and have 52 coded. The very first MPEG packet following thePreamble block is a control packet that contains system information.Following randomization and forward error correction processing, thedata packets are formatted into Data Frames for transmission and DataSegment Sync and Data Field Sync are added.

The ATSC-M/H data stream 200 is made up of bursts having a Preambleblock 210 followed by a predetermined number of Data Blocks 230appropriate for the selected data rate mode. According to the exemplaryembodiment, each Data Block 230 consists of 26 MPEG packets. Each DataFrame consists of two Data Fields, each containing 313 Data Segments.The first Data Segment of each Data Field is a unique synchronizingsignal (Data Field Sync) and includes the training sequence used by theequalizer in the receiver. The remaining 312 Data Segments each carrythe equivalent of the data from one 188-byte transport packet plus itsassociated FEC overhead. The actual data in each Data Segment comes fromseveral transport packets because of data interleaving. Each DataSegment consists of 832 symbols. The first 4 symbols are transmitted inbinary form and provide segment synchronization. This Data Segment Syncsignal also represents the sync byte of the 188-byte MPEG-compatibletransport packet. The remaining 828 symbols of each Data Segment carrydata equivalent to the remaining 187 bytes of a transport packet and itsassociated FEC overhead. These 828 symbols are transmitted as 8-levelsignals and therefore carry three bits per symbol. Thus, 828×3=2484 bitsof data are carried in each Data Segment, which is the requirement tosend a protected transport packet:

The ATSC M/H data stream consists of a sequence of blocks, each blockconsisting of 26 packets of the legacy VSB A/53 system. The ATSC M/Hdata stream is made up of bursts of blocks that each burst has aPreamble block followed by Nb Data Blocks, where Nb is a system variableparameter and a function of the overall ATSC M/H data rate to betransmitted. Each Data Block is encoded at one of the defined ATSC M/Hrate modes. This rate mode is applied to the entire Data Block. For eachburst of blocks, the Data Blocks are delivered such that the highestcoded FEC rates (i.e. the lowest fractional numbers) in the burst ofblocks will be delivered earliest and the lowest coded FEC rates (i.e.the highest fractional numbers) will be delivered the latest such thatstarting from a Preamble block, any following Data Blocks will haveequal or less robustness than the current Data Block. ATSC A/53 8VSBcoded legacy Data Blocks of 26 packets can be placed at one or moreblock for legacy overlay operation.

An enhancement to the ATSC or ATSC M/H transmission protocols that maybe especially advantageous to handheld or portable devices is the use ofdata packets of different coding within the same burst, such as, a Baselayer transmitted at one code rate and enhanced layer transmitted at ahigher rate. Under this scheme, a laptop, for example, would combine thetwo to show enhanced video, but a cellular telephone may only show thebase layer. This is advantageous as devices which require more robustcoding often have lower resolution displays. In an exemplary embodimentaccording to the present invention, the handheld data stream 200comprising preamble blocks 210 and data blocks 230. Data blocks 0 and 1may be coded at ¼ for base layer and blocks 10 and 11 coded at ½ forenhanced layer. Thus different code rates are transmitted in the sameburst.

In addition, a chirp signal can be used as a sequence for training theequalizer. Pattern interference is a problem when NTSC signals are beingtransmitted, but with the discontinued use of NTSC signals, the fixedpattern chirp signal will be acceptable. A chirp is a signal in whichthe frequency increases (‘up-chirp’) or decreases (‘down-chirp’) withtime. It is commonly used in sonar and radar, but has otherapplications, such as in spread spectrum communications. In spreadspectrum usage, SAW devices such as RACs are often used to generate anddemodulate the chirped signals. A linear chirp waveform is a sinusoidalwave that increases in frequency linearly over time.

Turning now to FIG. 3, a data frame 300 is shown according to thepresent invention is shown. The data frame 300 shown is organized fortransmission where each Data Frame consists of two Data Fields, eachcontaining 313 Data Segments. The first Data Segment of each Data Fieldis a unique synchronizing signal (Data Field Sync) and includes thetraining sequence used by the equalizer in the receiver. The remaining312 Data Segments each carry the equivalent of the data from one188-byte transport packet plus its associated FEC overhead. The actualdata in each Data Segment comes from several transport packets becauseof data interleaving. Each Data Segment consists of 832 symbols. Thefirst 4 symbols are transmitted in binary form and provide segmentsynchronization. This Data Segment Sync signal also represents the syncbyte of the 188-byte MPEG-compatible transport packet. The remaining 828symbols of each Data Segment carry data equivalent to the remaining 187bytes of a transport packet and its associated FEC overhead. These 828symbols are transmitted as 8-level signals and therefore carry threebits per symbol. Thus, 828×3=2484 bits of data are carried in each DataSegment, which exactly matches the requirement to send a protectedtransport packet:

-   -   187 data bytes+20 RS parity bytes=207 bytes    -   207 bytes×8 bits/byte=1656 bits    -   ⅔ rate trellis coding requires 3/2×1656 bits=2484 bits.

The exact symbol rate is given by equation 1 below:

S _(r)(MHz)=4.5/286×684=10.76 . . . MHz  (1)

The frequency of a Data Segment is given in equation 2 below:

f _(seg) =S _(r)/832=12.94 . . . ×10³ Data Segments/s.  (2)

The Data Frame rate is given by equation (3) below:

f _(frame) =f _(seg)/626=20.66 . . . frames/s.  (3)

The symbol rate S_(r) and the transport rate T_(r) shall be locked toeach other in frequency.

The 8-level symbols combined with the binary Data Segment Sync and DataField Sync signals is used to suppressed-carrier modulate a singlecarrier. Before transmission, however, most of the lower sideband shallbe removed. The resulting spectrum is flat, except for the band edgeswhere a nominal square root raised cosine response results in 620 kHztransition regions. At the suppressed-carrier frequency, 310 kHz fromthe lower band edge, a small pilot is added to the signal as describedpreviously.

Turning now to FIG. 4, an embodiment of a terrestrial broadcast receiver400 for mobile/handheld reception of the present disclosure is shown.The receiver 400 comprises a signal receiving element 410, a tuner 420,a pre-equalizer demodulator 430, a equalizer controller 440, anequalizer 450, a post-equalizer correction processor 460, a transportdecoder 470 and a tuner controller 480.

The signal receiving element 410 is operative to receive signalsincluding audio, video, and/or data signals (e.g., television signals,etc.) from one or more signal sources, such as a satellite broadcastsystem and/or other type of signal broadcast system. According to anexemplary embodiment, signal receiving element 410 is embodied as anantenna such as a log periodic antenna, but may also be embodied as anytype of signal receiving element. The antenna 410, of this exemplaryembodiment, is operative to receive ATSC M/H terrestrially transmittedaudio, video, and data signals over a frequency bandwidth. ATSC signalsare generally transmitted over the frequency range of 54 to 870 MHz,with a bandwidth of anywhere from approximately 6 MHz per channel. Subchannels may be time multiplexed The signal is coupled from the antennavie a transmission line such as a coaxial cable or printed circuit boardtrace.

The Tuner 420 is operative to perform a signal tuning functionresponsive to a control signal from the tuner controller 480. Accordingto an exemplary embodiment, the tuner 420 receives an RF signal from theantenna 410, and performs the signal tuning function by filtering andfrequency down converting (i.e., single or multiple stage downconversion) the RF signal to thereby generate an intermediate frequency(IF) signal. The RF and IF signals may include audio, video and/or datacontent (e.g., television signals, etc.), and may be of an analog signalstandard (e.g., NTSC, PAL, SECAM, etc.) and/or a digital signal standard(e.g., ATSC, QAM, QPSK, etc.). The tuner 420 is operative to convert thereceived ATSC M/H signal from the carrier frequency to an intermediatefrequency. For example, the tuner may convert a 57 MHz signal receivedat the antenna 410 to a 43 MHz IF signal. The Pre-Equalizer Demodulator430 is operative to demodulate the IF signal from the Tuner 420, to abaseband digital stream. The baseband digital stream then coupled to theequalizer.

The tuner controller 480 is operative receive instructions from thetransport decoder 470 in response to the signal level and frequency ofthe tuned channel or a desired tuned channel. The tuner controller 480generates a control signal in response to these received instructions tocontrol the tuner 420 operation.

The equalizer controller 440 is operative to generate an error term inresponse to the decoded data. This provides the ability for a datadirected equalizer. The equalizer controller 440 estimates the errorbetween the received data and the decoded data and generates an errorterm. The error term is fed to the equalizer 450 to be minimized.

The equalizer 450 is operative to receive the tuned and demodulated MPEGstream from the pre-equalizer demodulator 430 and calculates equalizercoefficients which are applied to an equalization filter within theequalizer to produce an error free signal. The equalizer 450 isoperative to compensate for transmission errors, such as attenuation andintersymbol interference. The equalizer comprises a matched filter whichperforms roll off filtering which is operative to cancel the intersymbolinterference. During the equalizer training period, a previously chosentraining signal is transmitted through the channel and a properlydelayed version of this signal, that is prestored in the receiver, isused as a reference signal. The training signal is usually apseudo-noise sequence long enough to allow the equalizer to compensatefor the channel distortions. The equalizer according to an exemplaryembodiment of the present invention is operative to store a plurality ofpseudo-noise sequences, wherein each pseudo-random sequence correspondsto a code rate. When the equalizer 450 receives the pseudorandomsequence training signal, the equalizer compares a portion of thereceived sequence with the plurality of stored sequences. When a matchis made, the code rate associated with the received sequence is used bythe decoder to decode the data received after the training sequence.

The first Data Segment of each Data Field is a synchronizing signal(Data Field Sync) that includes a training sequence used by theequalizer 450 in the receiver. As described above, an advantageousconfiguration may assign each pseudorandom sequence a different patternassociated with a unique code rate. The equalizer 450 will use thehighest matching correlator available to identify the code rate withinthe preamble. Utilization of the data segment for code rateidentification, in addition to equalizer training can provide vitalinformation for the receiver via the second mode of data delivery. Areceiver equipped to receive multiple training signals requires a uniquecorrelator for each code rate, however, using this technique providesfor a robust and efficient system. 63 symbols within the field syncpseudorandom sequence that are not defined by the ATSC standard can beconfigured to indicate the code rate.

Each pseudorandom sequence has a different pattern for code rate. Outputof different correlators, use the highest one. The highest oneidentifies the code rate with the preamble. Utilization of an existingsegment of the transmission system used primarily for training to alsoprovide vital information for the second mode of data delivery. Costs aunique correlator for each code rate. Idea is that you get a robustsystem that is efficient.

The post-equalizer correction processor 460 and transport decoder 470are operative to perform error correction and to decode the MPEG datastream. These elements are shown and discussed in detail in FIGS. 5 and6.

Turning now to FIG. 5, a block diagram of an embodiment of a decoder 500used in a receiver system is shown. Decoder 500 includes circuitry thatis adapted to use redundant packets, such as the non-systematic packetsin a data stream as described above, to aid in decoding data received bythe receiver. Decoder 500 is also generally capable of decoding datathat has been encoded using the legacy or existing A53 standard.

In decoder 500, following initial tuning, demodulation, and processingby other circuits (FIG. 4) a trellis decoder 502 receives the incomingsignal. The trellis decoder 502 is connected to a convolutionalde-interleaver 504. The output of the convolutional de-interleaver 504is connected to a byte-code decoder 506. The byte-code decoder 506 hasan output that is connected to a Reed-Solomon decoder 508. The output ofthe Reed-Solomon decoder 508 is connected to a de-randomizer 510. Thede-randominizer 510 output is connected to a data decoder 512. The datadecoder 512 provides an output signal for use in the remaining portionof the receiver system such as video display or audio reproduction.

In accordance with the existing or legacy A53 standard, the trellisdecoder 502 includes a signal de-multiplexer, twelve ⅔-rate trellisdecoders and a signal multiplexer. The de-multiplexer distributes thedigital samples among the twelve ⅔-rate trellis decoders and themultiplexer multiplexes the estimates generated byte each of the twelve⅔-rate trellis decoders. A de-interleaver 504, such as a convolutionalinterleaver, de-interleaves the stream of trellis-decoded bit estimates,producing sequences or packets arranged to include 207 bytes. The packetarrangement is performed in conjunction with the determination andidentification of the location of the synchronization signals, notshown. A Reed-Solomon error correction circuit 508 considers eachsequence of 207 bytes produced by the de-interleaver 504 as one or morecodewords and determines if any bytes in the codewords or packets werecorrupted due to an error during transmission. The determination isoften performed by calculating and evaluating a set of syndromes orerror patterns for the codewords. If corruption is detected, theReed-Solomon error correction circuit 508 attempts to recover thecorrupted bytes using the information encoded in the parity bytes. Theresulting error-corrected data stream is then de-randomized by ade-randomizer 510 and thereafter provided to a data decoder 512 thatdecodes the data stream in accordance with the type of content beingtransmitted. Typically, the combination of the trellis decoder 502, thede-interleaver 504, the Reed-Solomon decoder 508, and the de-randomizer510 are identified as an 8-VSB decoder within a receiver. It isimportant to note that, in general, the typical receiver for receivingsignals compliant with the legacy A53 standard performs the receivingprocess in the reverse order of the transmitting process.

The received data, in the form of bytes of data in data packets, isdecoded by trellis decoder 502 and de-interleaved by de-interleaver 504.The data packets may include 207 bytes of data and further may begrouped in groups or 24, 26, or 52 packets. The trellis decoder 502 andde-interleaver 20504 are capable of processing incoming legacy formatdata as well as byte-code encoded data. Based on a predetermined packettransmission sequence that is also known by the receiver, the byte-codedecoder 506 determines if the packet is a packet included in a byte-codeencoded or robust data stream. If the received packet is not from thebyte-code encoded data stream then the received packet is provided tothe Reed-Solomon decoder 508 without any further processing in byte-codedecoder 506. Byte code decoder 506 may also include a de-randomizer thatremoves the known sequence of constants multiplied by or added to thedata stream during encoding. It is important to note that a rugged datastream includes both systematic packets and bytes that are identical tothe original data and non-systematic packets and bytes that containredundant data.

If the byte-code decoder 506 determines that the received is a byte-codeencoded packet belonging to robust or rugged data stream, the packet maybe decoded along with other packets comprising the same data stream. Inone embodiment, byte-code encoded packets of the same data stream aredecoded by multiplying each byte within the packet by the inverse of thevalue of the element that was used to develop the byte-coded packet. Thedecoded values of the bytes of the non-systematic packet are compared tothe values of the bytes of the systematic packet and the values of anybytes in the two packets that are not identical may be erased (i.e., setto zero) in the systematic packet or may be replaced by the informationin the non-systematic packet. The systematic packet with error byteserased may thereafter be decoded using Reed-Solomon decoding performedin Reed-Solomon decoder 508. Further description of other embodiments ofbyte-code decoders will be discussed below.

Byte code decoder 506 may also be adapted to operate as a block coderfor decoding signals encoded as shown in FIG. 1. For instance, byte codedecoder 506 may include a packet interleaver similar to packetinterleaver 120 and a packet deinterleaver similar to packetdeinterleaver 130. Additionally, the byte code encoder function may beadapted to decode a GF(256) Serial Concatenated Block Coded (SCBC)signal. The byte code decoder 506 may further include an identifierblock used for identifying data encoded for mobile or ATSC M/H receptionand/or identification of a-priori training packets. Additionally, theidentifier block may include a packet identifier block to determine, forexample, if the headers in the incoming packets include a PID used formobile reception.

It is important to note that in a preferred encoder byte-code encodingprecedes the Reed-Solomon encoding of data packets. However, in decoder500 shown here, the incoming data is byte-code decoded before being theReed-Solomon decoded. The re-ordering is possible because both thebyte-code operation and Reed-Solomon code operation are linear over theGalois Field(256) used in the A53 standard, and linear operators arecommutative in a Galois Field. It is advantageous to do block decodingfirst before the Reed Solomon because there are soft decoding algorithmswhich make it practical to have an iterative decoding algorithm. Theimportance of the re-ordering is important because the byte-codeencoding provides a soft decoding algorithm, which then makes possibleiterative decoding or turbo decoding, which has higher reliability forrecovering errors in the received signal. As a result, performingbyte-code decoding prior to Reed-Solomon decoding results in improvedreceiver performance as measured in terms of bit-error rate and signalto noise ratio

Turning now to FIG. 6, a block diagram of another embodiment of adecoder 600 used in a receiver is shown. Decoder 600 includes additionalcircuitry and processing for receiving and decoding signals that havebeen adversely affected by transmission of the signal over atransmission medium such as electromagnetic waves over the air. Decoder600 is capable of decoding both a rugged data stream as well as a legacydata stream.

In decoder 600, the incoming signal, following initial processing, isprovided to equalizer 606. Equalizer 606 is connected to trellis decoder610, which provides two outputs. A first output from trellis decoder 610provides feedback and is connected back as a feedback input to equalizer606. The second output from trellis decoder 610 is connected to aconvolutional de-interleaver 614. The convolutional de-interleaver 614is connected to a byte-code decoder 616, which also provides twooutputs. A first output from byte-code decoder 616 is connected back asa feedback input to trellis decoder 610 through a convolutionalinterleaver 618. The second output from byte-code decoder 616 isconnected to a Reed-Solomon decoder 620. The output of the Reed-Solomondecoder 620 is connected to de-randomizer 624. The output of thede-randomizer 624 is connected to a data decoder 626. Reed-Solomondecoder 620, de-randomizer 624, and data decoder 626 are connected, andfunctionally operate, in a manner similar to Reed-Solomon,de-randomizer, and data decoder blocks described in FIG. 5 and will notbe further described here.

An input signal from the front end processing (e.g. antenna, tuner,demodulator, A/D converter) of the receiver (not shown) is provided toequalizer 606. Equalizer 606 processes the received signal to completelyor partially remove the transmission channel effect in an attempt torecover the received signal. The various removal or equalization methodsare well known to those skilled in the art and will not be discussedhere. Equalizer 506 may include multiple sections of processingcircuitry including a feed-forward equalizer (FFE) section and adecision-feedback-equalizer (DFE) section.

The equalized signal is provided to trellis decoder 610. The trellisdecoder 610 produces, as one output, a set of decision values that areprovided to the DFE section of equalizer 606. The trellis decoder 610may also generate intermediate decision values that are also provided tothe DFE section of equalizer 606. The DFE section uses the decisionvalues along with intermediate decision values from the trellis decoder610 to adjust values of filter taps in equalizer 606. The adjustedfilter tap values cancel interference and signal reflections that arepresent in the received signal. The iterative process allows equalizer606, with the assistance of feedback from trellis decoder 610, todynamically adjust to a potential changing signal transmissionenvironment conditions over time. It is important to note that theiterative process may occur at a rate similar to incoming data rate ofthe signal, such as 19 Mb/s for a digital television broadcast signal.The iterative process also may occur at a rate higher than the incomingdata rate.

The trellis decoder 610 also provides a trellis decoded data stream toconvolutional de-interleaver 614. Convolutional de-interleaver 614operates similar to the de-interleaver described in FIG. 5 generatesde-interleaved bytes organized within data packets. The data packets areprovided to byte-code decoder 5616. As described above, packets that arenot a part of a rugged data stream are simply passed through thebyte-code decoder 616 to Reed-Solomon decoder 620. If the byte-codedecoder 616 identifies a group of the packets as part of a rugged datastream, the byte-code decoder 616 uses the redundant information in thenon-systematic packets to initially decode the bytes in the packets asdescribed above.

Byte-code decoder 616 and the trellis decoder 610 operate in aniterative manner, referred to as a turbo-decoder, to decode the ruggeddata stream. Specifically, the trellis decoder 610 provides, afterde-interleaving by convolutional de-interleaver 614, a first softdecision vector to the byte-code decoder 616 for each byte of thepackets that are included in the rugged data stream. Typically, thetrellis decoder 610 produces the soft decision as a vector ofprobability values. In some embodiments, each probability value in thevector is associated with a value that the byte associated with thevector may have. In other embodiments, the vector of probability valuesis generated for every half-nibble (i.e., two bits) that is contained inthe systematic packet because the ⅔-rate trellis decoder estimatestwo-bit symbols. In some embodiments the trellis decoder 610 combinesfour soft decisions associated with four half-nibbles of a byte toproduce one soft-decision that is a vector of the probabilities ofvalues that the byte may have. In such embodiments, the soft-decisionscorresponding to the byte is provided to the byte-code decoder 616. Inother embodiments, the byte-code decoder separates a soft-decisionregarding a byte of the systematic packet into four soft-decisionvectors, wherein each of the four soft-decisions is associated with ahalf-nibble of the byte.

The byte-code decoder 616 uses the soft decision vector associated withthe bytes comprising packets of the rugged data stream to produce afirst estimate of the bytes that comprise the packets. The byte-codedecoder 616 uses both the systematic and the non-systematic packets togenerate a second soft decision vector for each byte of packetscomprising the rugged stream and provides the second soft-decisionvector to the trellis decoder 610, after re-interleaving byconvolutional interleaver 618. The trellis decoder 610 thereafter usesthe second soft-decision vector to produce a further iteration of thefirst decision vector, which is provided to the byte-code decoder 616.The trellis decoder 610 and the byte-code decoder 616 iterate in thisfashion until the soft-decision vector produced by the trellis decoderand byte-code decoder converge or a predetermined number of iterationsare undertaken. Thereafter, the byte-code decoder 616 uses theprobability values in the soft-decision vector for each byte of thesystematic packets to generate a hard decision for each byte of thesystematic packets. The hard decision values (i.e., decoded bytes) areoutput from the byte-code encoder 616 to Reed-Solomon decoder 620. Thetrellis decoder 610 may be implemented using a Maximum a Posteriori(MAP) decoder and may operate on either byte or half-nibble (symbol)soft decisions.

It is important to note that turbo-decoding typically utilizes iterationrates related to passing decision data between blocks that are higherthan the incoming data rates. The number of possible iterations islimited to the ratio of the data rate and the iteration rate. As aresult and to the extent practical, a higher iteration rate in theturbo-decoder generally improves the error correction results. In oneembodiment, an iteration rate that is 8 times the incoming data rate maybe used.

A soft input soft output byte-code decoder such as described in FIG. 6may include vector decoding functions. Vector decoding involves groupingbytes of the data including systematic and non-systematic bytes. Forexample, for a rate ½ byte code encoded stream, 1 systematic and 1non-systematic byte will be grouped. The two bytes have over 64,000possible values. The vector decoder determines or estimates aprobability for each of the possible values of the two bytes and createsa probability map. A soft decision is made based on a weighting theprobabilities of some or all of the possibilities and the Euclideandistance to a possible codeword. A hard decision may be made when theerror of the Euclidean distance falls below a threshold.

Byte-code decoders, as described in FIGS. 5 and 6 may decode a ruggeddata stream that has been encoded by the byte-code encoders describedearlier, including encoding by simple byte-code encoders or concatenatedbyte-code encoders. The byte-code decoders in FIGS. 5 and 6 describedecoding a rugged data stream encoded by a simple or constituentbyte-code encoder involving only a single encoding step. Concatenatedbyte-code decoding includes decoding the incoming codewords or bytes inmore than one decoding step in addition to intermediate processing suchas de-interleaving, de-puncturing, and re-insertion.

Referring now to FIG. 7, a state diagram of an exemplary embodiment of amethod of encoding according to the present invention is shown. Themethod 700 for encoding data according to an exemplary embodiment of thepresent invention comprises the following states. First, the deviceenters a wait state to start 710. The device then encodes the data intoa first format 720 wherein the first format may be a VSB or QAM formatand encoded according to a code rate. The code rate indicates the numberof redundant packets generated by the encoder compared to the number ofdata packets encoded. The device then generates a packet ID 730. Thedevice then packetizes the data and the packet ID in a packet 740. Thedevice then transmits the packet 750 and returns to the wait state 710.

Referring now to FIG. 8, a state diagram of an exemplary embodiment of amethod 800 of decoding according to the present invention is shown. Thedevice first enters a wait state where it waits to receive a packet 810.The device then receives a packet comprising data and a packetidentifier 820. The device then proceeds to determine a code rate inresponse to a portion of said packet identifier 830. The device, ifappropriately equipped then decodes the data within the packet accordingto said code rate 840. The device then returns to the wait state.

Referring now to FIG. 9, a state diagram of an exemplary embodiment of amethod 900 of encoding according to the present invention is shown. Thedevice first enters a wait state where it waits for data to encode 910.After receiving data, the device encodes said data according to one of aplurality of code rates 910. The device then packetizes the data fortransmission 920. The device encodes a training sequence where thetraining sequence indicative of said one of a plurality of code rates.The device then transmits the training sequence 930. The device thentransmits the 940. An encoder operative according to this method maycomprise a processor for generating a training sequence and a packet,said packet comprising at least one data, said at least one data encodedaccording to a first format, and wherein said training sequence beingindicative of said first format.

Referring now to FIG. 10, a state diagram of an exemplary embodiment ofa method 1000 of decoding according to the present invention is shown.The device first enters a wait state where it waits to receive atraining sequence 1010. The device then receives a training sequence1020. Upon receiving the training sequence, the device determines a coderate in response to a portion of said training sequence 1020. In anexemplary embodiment, each code rate is associated with a uniquetraining sequence. When the device, such as a receive or a decoder,receives the unique training sequence, it can associate the trainingsequence with a stored code rate, thereby facilitating the device toanticipate the code rate any incoming data to be received shortly. Thedevice then receives the packet comprising data 1040. The device thendecodes the data according to the code rate determined from the trainingsequence 1050. A decoder according to the method would comprise aprocessor for receiving a training sequence and a packet, said packetcomprising at least one data, said processor being further operative toidentify a code rate associate with said training sequence and to decodesaid at least one data in accordance with said to a code rate.

Referring now to FIG. 11, a state diagram of an exemplary embodiment ofa method 1100 of encoding according to the present invention is shown.The device first enters a wait state where it waits for data to encode1110. Upon receiving the data, the device encodes the data according toa code rate 1120. The device then generates a packet, where the packetcomprising said data and a packet identifier. 1120 The packet identifiercomprising an indicator indicating said one of a plurality of coderates. The device then generates a training sequence, said trainingsequence indicative of said one of a plurality of code rates 1150. Thedevice then optionally transmits, or couples to a transmitter, thetraining sequence for transmission 1140. The device then optionallytransmits, or couples to a transmitter, the packet for transmission1150. The device may then optionally return to the wait state 1110. Anencoder operative according to the described method may comprise aprocessor for generating a training signal and a packet, said packetcomprising a packet identifier and data frame, said data frame encodedaccording to a first format, and wherein a portion of said packetidentifier indicative of said first format and said training signalbeing indicative of said first format.

Referring now to FIG. 12, a state diagram of an exemplary embodiment ofa method 1200 of decoding according to the present invention is shown.The device receives the training sequence 1210. The device thendetermines a code rate according to the training sequence 1220. Thisdetermination can be made mathematically, or through a look up table bycomparing the received training sequence to a stored training sequenceand then, upon a match, determined the code rate associated with thestored training sequence. The device then receives a packet comprisingdata and a packet identifier 1230. The device then determines a coderate in response to at least one of a portion of said training sequenceand a portion of said packet identifier 1240. The device then decodesthe data according to said code rate. 1250 The device can the optionallyreturn to the wait state 1210. A decoder operative according to thedescribed method may comprise a processor operative to receive atraining sequence and a packet, said packet comprising a packetidentifier, said processor further operative to decode data inaccordance with a code rate, said code rate determined in response to atleast one of said training sequence and said packet identifier forprocessing a packet, said packet comprising at least one data and apacket identifier.

Referring now to FIG. 13, a state diagram of an exemplary embodiment ofa method 1300 of encoding according to the present invention is shown.Upon receiving data to encode, the device first encodes a first portionof said data at a first code rate 1310. The device then encodes a secondportion of said data at a second code rate 1320. The device then encodessaid first portion of data and said second portion of data within afirst burst 1330. The device is then operative to transmit 1340, orcouple to a transmitter, the burst. An encoder operative to perform thismethod may comprise a processor operative to encode a first portion ofsaid data at a first code rate and a second portion of said data at asecond code rate and to encode said first portion of data and saidsecond portion of data into a first burst.

Referring now to FIG. 14, a state diagram of an exemplary embodiment ofa method 1400 of decoding according to the present invention is shown.The device first receives a burst 1410. The device is then operative todecoding a first portion of said data according to a first code rate1420. The device may optionally then decode a second portion of saiddata according to a second code rate 1430. The device may then combinethe first data and the second data 1440. This combined data mayoptionally be used to generate an image 1450. A decoder operative toimplement this method may comprise a processor operative to receive aburst comprising data, to decode a first portion of said data accordingto a first code rate, and to decode a second portion of said dataaccording to a second code rate.

A burst is any relatively high-bandwidth transmission over a shortperiod of time. For example, a download might use 2 Mbit/s on average,whilst have “peaks” bursting up to, say, 2.4 Mbit/s. A burst may also bea transmission that combines a very high data signaling rate with veryshort transmission times—i.e., the message is compressed. This has thedesirable advantage of allowing the receiver to turn on only duringburst periods, thus saving power over an operational time period. Thisis especially advantageous in handheld and portable devices, such asATSC M/H receivers and processors.

Operation of a data network in which data transmission is interrupted atintervals. Referring now to FIG. 15, a state diagram of an exemplaryembodiment of a method 1500 of encoding according to the presentinvention is shown. The device first encodes data according to a dataformat, such as 8 VSB or QAM 1510. The device then packetizes the dataaccording to a transmission format, such as ATSC M/H 1520. The devicethen generates a training sequence comprising a chirp pattern 1530. Thedevice then transmits, or couples to a transmitter, the trainingsequence 1540. The device then transmits, or couples to a transmitter,the packet 1550. An apparatus operative to implement this method maycomprise a processor operative to generate a training sequencecomprising a chirp pattern and a transmitter for transmitting saidtraining sequence.

A decoder for receiving the above transmitted training sequence maycomprise an equalizer for filtering a training signal and a data stream,said training signal comprising a chirp pattern, an equalizer controllerfor controlling said equalizer and for adjusting at least one equalizerweight in response to said training sequence and a decoder for decodingsaid data stream. The decoder may decode the signal by receiving atraining sequence; said training sequence comprising a chirp pattern,adjusting at least one equalizer weight in response to said trainingsequence, receiving a packet comprising data; and decoding said dataaccording to said code rate.

A chirp is a signal in which the frequency increases (‘up-chirp’) ordecreases (‘down-chirp’) with time. It is commonly used in sonar andradar, but has other applications, such as in spread spectrumcommunications. In spread spectrum usage, SAW devices such as RACs areoften used to generate and demodulate the chirped signals. In optics,ultrashort laser pulses also exhibit chirp due to the dispersion of thematerials they propagate through. A linear chirp waveform; a sinusoidalwave that increases in frequency linearly over timeIn a linear chirp,the instantaneous frequency f(t) varies linearly with time: f(t)=f0+ktwhere f0 is the starting frequency (at time t=0), and k is the rate offrequency increase or chirp rate.

In a geometric chirp, also called an exponential chirp, the frequency ofthe signal varies with a geometric relationship over time. In otherwords, if two points in the waveform are chosen, t1 and t2, and the timeinterval between them t2-t1 is kept constant, the frequency ratiof(t2)/f(t1) will also be constant. In an exponential chirp, thefrequency of the signal varies exponentially as a function of time:f(t)=f0kt where f0 is the starting frequency (at t=0), and k is the rateof exponential increase in frequency. Unlike the linear chirp, which hasa constant chirp rate, an exponential chirp has an exponentiallyincreasing chirp rate.

While the present invention has been described in terms of a specificembodiment, it will be appreciated that modifications may be made whichwill fall within the scope of the invention. For example, variousprocessing steps may be implemented separately or combined, and may beimplemented in general purpose or dedicated data processing hardware.Furthermore, various encoding or compression methods may be employed forvideo, audio, image, text, or other types of data. Also, the packetsizes, rate modes, block coding, and other information processingparameters may be varied in different embodiments of the invention.

1-13. (canceled)
 14. A method of encoding data comprising the steps of:encoding a first portion of said data at a first code rate; encoding asecond portion of said data at a second code rate; encoding said firstportion of data and said second portion of data within a first burst.15. A method of receive data comprising the steps of: receiving a burstcomprising data decoding a first portion of said data according to afirst code rate; and decoding a second portion of said data according toa second code rate.
 16. The method of claim 15 further comprising thestep of combining said decoded first portion of data and said decodedsecond portion of data into a first image.
 17. A decoder comprising; aprocessor operative to receive a burst comprising data, to decode afirst portion of said data according to a first code rate, and to decodea second portion of said data according to a second code rate.
 18. Thedecoder of claim 17 further operative to combine said decoded firstportion of data and said decoded second portion of data into a firstimage.
 19. An encoder for encoding data comprising; a processoroperative to encode a first portion of said data at a first code rateand a second portion of said data at a second code rate and to encodesaid first portion of data and said second portion of data into a firstburst. 20-23. (canceled)